Homeowners Professionals

How does a temperature sensor work?

Temperature sensors can be very beneficial, and even necessary, for a number of applications and you may use them more often than you think. How often do you check the weather forecast to find the predicted temperature for the day or check that your oven is up to the correct heat? They’re particularly important to help keep us safe - for example, we can probe food to make sure that it’s cooked on the inside and check the temperature of our car engine to ensure it’s not overheating.

In this article, we’ve explained how temperature sensors work, particularly within your heating system, and we offer guidance on how to check whether it’s showing the right reading.  

How do temperature sensors work?

Before we can begin to explain how temperature sensors work, we must first explain the different types of sensors you can have.

There are two categories that the sensors can fall into - contact and noncontact. A contact temperature sensor will physically touch the object to check its temperature. An example of this could be a food probe. A noncontact temperature sensor measures the area around a heat source, such as a room thermostat. There are lots of types of temperature sensors that work in different ways, but every type will fall within these two categories. Some examples of temperature sensors include thermocouples, thermistors and infrared sensors. We look in more depth at each one below.

A thermocouple is made from two dissimilar metals that are joined together. One metal is able to measure a constant ‘cold’ temperature. The other metal can determine the temperature of the object you’re trying to measure. When this second metal is heated, a continuous current is able to flow through the thermoelectric circuit. A voltage is created and the thermocouple is able to determine the temperature based on the amount of voltage that is produced.

An infrared temperature sensor works in a very different way to a thermocouple. Photodetectors are used to find infrared energy that is emitted by an object. These detectors can convert that infrared energy into an electric signal, which provides an accurate temperature reading of the object. The higher the electrical signal, the higher the temperature of the object or room. This type of sensor is a non contact one. It can be used to track the temperature of moving objects, such as tyres and is ideal in situations where you don’t want to touch the object you’re measuring. A good example of this is ear thermometers. The eardrum is very sensitive and touching it could damage it, therefore ear thermometers are infrared.

NTC Thermistors work in a similar way to thermocouples and are used in gas boilers, they’re made using metals that are highly sensitive to changes in temperature. The resistance, or lack of electrical current, in a thermistor decreases as the temperature increases. This resistance can be measured to determine the temperature of a room liquid or object. It is this kind of sensor that can be found in a digital thermostat. The thermostat runs an electrical current through the thermistor and measures the resistance to determine the temperature of the room

Is a temperature sensor an input or output device?

An output device is any device that sends data to a computer or human. It sends data in a readable form that can be processed. This means that a temperature sensor is an output device because it’s providing you with additional data that you didn’t know before. 

How to check a thermostat

If you think that your thermostat isn’t providing you with an accurate reading of your home’s temperature, it could need replacing. However, before you replace it, here’s a quick test that you can do to see if your thermostat really is showing the correct reading.

You should locate your room thermostat. It’s most likely to be on an inside wall away from any windows and radiators. Once you’ve found it, you need to take a glass thermometer and tape it to the wall, making sure that there’s a small piece of cloth between the thermometer and the wall for an accurate reading. Leave the thermometer for 15 minutes and then check its temperature. It should register almost exactly the same as your thermostat.

If the readings are considerably different, your thermostat may need replacing.

You may need an engineer to check that the thermostat doesn’t need cleaning. Dirt that’s trapped between the connections can be a cause of a faulty reading.  

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